* java.util.concurrent.CompletableFuture#thenAcceptAsync}.
   *
   * @param callback The callback to invoke when this {@code Future} is completed.
   * @param executor The executor to run {@code callback} when the future completes.
   */
  public final void addCallback(FutureCallback<? super V> callback, Executor executor) {
    Futures.addCallback(this, callback, executor);
  }

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

                notifyStarted();
                // We need to wait for the main thread to leave the ServiceManager.startAsync call
                // to
                // ensure that the thread running the failure callbacks is not the main thread.
                Uninterruptibles.awaitUninterruptibly(afterStarted);
                notifyFailed(new Exception("boom"));
              }
            }.start();
          }

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

                notifyStarted();
                // We need to wait for the main thread to leave the ServiceManager.startAsync call
                // to
                // ensure that the thread running the failure callbacks is not the main thread.
                Uninterruptibles.awaitUninterruptibly(afterStarted);
                notifyFailed(new Exception("boom"));
              }
            }.start();
          }

import javax.annotation.CheckForNull;

/**
 * Base class for implementing services that can handle {@link #doStart} and {@link #doStop}
 * requests, responding to them with {@link #notifyStarted()} and {@link #notifyStopped()}
 * callbacks. Its subclasses must manage threads manually; consider {@link
 * AbstractExecutionThreadService} if you need only a single execution thread.
 *
 * @author Jesse Wilson
 * @author Luke Sandberg
 * @since 1.0
 */

  public void testOr_supplier_present() {
    assertEquals("a", Optional.of("a").or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_supplier_absent() {
    assertEquals("fallback", Optional.absent().or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_nullSupplier_absent() {

   * for bridge methods.
   */
  public void testRegistrationWithBridgeMethod() {
    final AtomicInteger calls = new AtomicInteger();
    bus.register(
        new Callback<String>() {
          @Subscribe
          @Override
          public void call(String s) {
            calls.incrementAndGet();
          }
        });

    bus.post("hello");

   * for bridge methods.
   */
  public void testRegistrationWithBridgeMethod() {
    final AtomicInteger calls = new AtomicInteger();
    bus.register(
        new Callback<String>() {
          @Subscribe
          @Override
          public void call(String s) {
            calls.incrementAndGet();
          }
        });

    bus.post("hello");

  }

  /**
   * This tests for a bug where if {@link Service#stopAsync()} was called while the service was
   * {@link State#STARTING} more than once, the {@link Listener#stopping(State)} callback would get
   * called multiple times.
   */
  public void testManualServiceStopMultipleTimesWhileStarting() throws Exception {
    ManualSwitchedService service = new ManualSwitchedService();